学士学位论文—-基于单片机的超声波测距电路的研究.doc

目录

设计总说明：...............................................................................................................................................3

ABSTRACT:.................................................................................................................................................5

第一章：超声波测距原理论述...............................................................................................................7

1.1 超声波介绍...................................................................................................................7

1.2 超声波测距系统概述...................................................................................................9

1.3 超声波测距的基本原理............................................................................................11

2.5 系统控制和复位........................................................................................................20

2.6 看门狗定时器............................................................................................................20

2.7 ATmega16 的中断向量（外部中断）......................................................................20

2.8 具有 PWM 功能的 8 位定时器/ 计时器....................................................................21

2.9 比较输出模式和波形产生........................................................................................22

2.10 T/C0 与 T/C1 的预分频器.....................................................................................24

2.11 串行外设接口－ SPI..............................................................................................24

2.12 串行外设接口－USART............................................................................................25

2.13 模数转换器..............................................................................................................25

2.14 JTAG 接口和片上调试系统....................................................................................26

3.6 温度补偿电路.............................................................................................................31

3.6.1 温度计算...........................................................................................................33

3.6.2 DSl820 工作过程命令.......................................................................................33

3.6.3 时 序..................................................................................................................33

3.6.4 写时间隙............................................................................................................34

3.6.5 读时间隙............................................................................................................34

3.6.6 多路测量............................................................................................................34

3.7 在线通信电路设计......................................................................................................35

第四章，超声波发射电路及接收电路的设计 .................................................................................36

4.1 超声波发射电路...............................................................................................................................36

第五章软件设计 ........................................................................................................................................43

5.1 主程序流程图..............................................................................................................43

5.2 发射子程序设计..........................................................................................................44

5.3 温度测量子程序..........................................................................................................44

5.4 测量子程序..................................................................................................................46

5.5 计算子程序..................................................................................................................46

5.6 显示驱动子程序..........................................................................................................47

5.7 报警子程序..................................................................................................................47

第六章 设计心得......................................................................................................................................49

致 谢.............................................................................................................................................................50

基于单片机的超声波测距电路的研究

统，本系统发射器对着一个物体发射一定频率的超声波同时接收同频率的超声波，单片

机通过计算从超声波发射时刻到接收返回的超声波时刻从而确定超声波通过的时间，根

据房间的温度来确定超声波在空气中的速度大概是 340m/s , AVR 单片机计算二者的距离

同时用 3 个 LED 驱动电路驱动的 LED 来显示，显示距离误差大概是±1cm，最小能测量

时 1cm 同时局限于发射器的传感器的设定时间，最大能测量 4m，超声波测距发射距离决

定与发射物的材质和形状，例如超声波可能被地毯吸收，这样测量的距离就大大的降低，

假如反射波接收的频率太低就可能不被系统处理，这样显示就会出现错误。

本设计用来发射和接收超声波的设备是 40hz 压电陶瓷超声波传感器，AVR ATMEGA16

单片机驱动超声波发射器 40hz 的方波来源于晶振,波接收器接收回波 由于 AVR

我们可以通过 DS18B20 芯片来确定室温，精确的确定超声波的速度，二者的距离通过 AVR

ATMEGA16 精确的计算同时在 3 个数码管上显示出来，一旦显示出来，单片机就进入休眠

状态来节省电力能源。这篇设计的主要电路分析。

传感器的输出驱动电路直接由 9V 电池供电并提供驱动超声波发射器由一个二进制

非门 CD4049 电路实现的。其中一个非门用来为驱动器的一侧提供 180 度的相移信号。

另一侧由相内信号驱动。这种结构使输出端的电压提高了一倍，为发射传感器提供了足

够的电压。两个门并联连接以便每一侧能够为传感器提供足够的驱动电流。电容耦合阻

断了到传感器的直流通路。因为 CD4049 工作于 9V 而 AVR ATMEGA16 工作于 Vcc=5V。 AVR

ATMEGA16 和输出驱动器之间的逻辑电平是不匹配的，可以双极性晶体管就作为这两种逻

辑电平之间的转换器。

度传感器测温电路，采取声速预置和媒质温度测量相结合的办法对声速进行修正，降低

了温度变化对测距精度的影响。针对噪声环境中超声波测距的情况，本文讨论了一种基

于时延的估计方法，可有效地降低噪声对测距的干扰，有利于提高超声波测距系统的测

量精度。

关键词：超声波测距 AVR atmega16 DS18B20

ABSTRACT: In different occasions , the demands of the precision on ultrasonic distance

measuring system are different .Usually , the error of the ultrasonic distance measuring

system is large , so they cannot be satisfied with the demands in some occasions. This article

takes temper A Ture account into the ult rasonic distance measuring system and makes it have

higher precision han before and increases the function of broadcasting the result . It can apply

sound in air at room temperature to be 340m/s, the AVR atmega16 computes the distance

between the system and the subject and displays it using a three-digit static LED driven by its

integrated LED driver. The distance is displayed in inches with an accuracy of ±1 cm. The

minimum distance that this system can measure is 1cm and is limited by the transmitter’s

transducer settling-time. The maximum distance that can be measured is 4m. The amplitude

of the echo depends on the reflecting material, shape, and size. Sound-absorbing targets such

as carpets the maximum measurable range is lower for such subjects. If the amplitude of the

echo received by the system is so low that it is not detectable by the Comparator the system

goes out of range. This is indicated by displaying the error message

1 Theory of Operation

the speed of sound in air is v=340m/s at room temperature and that the measured time taken

for the sound waves to travel the distance from the source to the subject and back to the

source is seconds,as we know：